Towards Model-Based Specification and Safety Assurance of Nuclear I&C Systems: Applicability of SYSML and AADL

Complexity of modern control and safety systems challenge the usual linear document-based presentation of system design. This complicates the work of designers, assessors and regulators comprehending the system, whose understanding often depends on building a mental model of the system and thus assessing its suitability. More rigorous and structured way to represent the system, than the linear documents-based, is model-based approach. Based on a literature review, SysML and AADL were identified as suitable candidates. They were tried in an exploratory case study modelling APR1400 reactor protection system, based on its linear description from a real applicant’s design control document. Effort was also taken to extract safety assurance information (for independence) from the documentation and organize it into a structured safety argument. Research serves also to discuss the strengths and weaknesses of model-based specification and assessment compared to document-based approaches. Modelling of the system based on design document and extracting safety assurance information was challenging. Results, based on the modelling experiences and literature review, argue that the studied architecture languages offer benefits over the use of natural language in clarity, ambiguity and traceability. However, using these architecture description languages require extensive modelling expertise and effort to allow a smooth modelling process and understanding. In addition, multidisciplinary insight into the system at both the conceptual level as well as hardware and software level is required. We also identified support of classical safety analysis methods within SysML and AADL.